CT and MRI mammography are currently the most effective breast cancer screening techniques. Conventional mammography techniques rely on a pair of 2D X-ray images of the female breast, taken from two different directions: from the top to the bottom and from one side to the other. The breast tissue to be examined is compressed and held between two glass plates to ensure that the whole breast tissue is viewed. Nowadays, full-field digital mammography (FFDM) systems are commonly used which are e.g. based on real-time amorphous silicon (α-Si) or amorphous selenium (α-Se) flat panel detector (FPD) technology.
Although it has been shown in numerous clinical studies that mammography helps to achieve a reduction of breast cancer mortality rate by 30% to 50%, mammography is not a perfect imaging technique, which is due to the fact that about 30% of breast cancers are typically missed. Interpreting a mammogram is difficult due to superimpositions of the breast tissue, which makes small cancerous tissue regions and other pathological tissue anomalies sometimes undetectable. In clinical breast imaging, tumors and other tissue anomalies can be obscured by normal breast-tissue elements lying outside a plane of interest, thus leading to false-negative results and decreasing sensitivity. Conversely, superimposed tissue elements are known to give the appearance of a tissue abnormality and may lead to false-positive lesions that appear like a cancerous tumor on a mammogram, which is one reason for unnecessary call-backs of the patient in conventional 2D mammography.
In contrast to conventional 2D mammography, digital breast tomosynthesis (DBT) is an exciting new development in breast imaging which yields multiple high-resolution image slices located at different depth in a breast volume. DBT thereby provides three-dimensional structural information of the female breast by reconstructing (e.g. based on a standard inverse 3D Radon transform in conjunction with the filtered backprojection algorithm) a volumetric view from a series of e.g. eleven low-dose two-dimensional projection images of a compressed breast acquired at multiple projection angles during a sweep of the X-ray tube over a circular arc segment of e.g. 50°. Objects at different heights in the breast are projected differently at different angles. The subsequent image reconstruction leads to a stack of slice images of the different depth layers parallel to the detector surface. The in-slice resolution is predominantly determined by the detector resolution and usually much higher than the resolution between different slices (“depth resolution”) due to the incomplete sampling of the object within a relatively small angular scan range. This technique enables physicians to “page through” the interior of the female breast without obstruction by surrounding superimposed tissue.
As a result, DBT greatly reduces the problems of superimposed tissue that may obscure tumors or create the illusion of cancer. Other researchers have investigated tomosynthesis for applications such as angiography, chest imaging, hand joint imaging and dental imaging. The diagnostic capability of DBT may be further improved by the use of contrast agent providing “functional” information of the breast lesion.
However, since DBT volumetric images are computed using a complex algorithm known as maximum-likelihood expectation maximization (MLEM), the DBT method involves vast amounts of computation, which previously took far too long for being applied in a clinical setting. Nonetheless, early results with DBT are promising. Researchers believe that this novel breast imaging technique will make breast cancers easier to see in dense breast tissue and will make breast screening more comfortable.
Not only have the researchers shown that they will be able to find more cancers earlier, but they will also be able to reduce many of the false alarms that occur when using conventional mammography due to the overlap of normal structures in the breast. DBT virtually eliminates these false-positive studies. This will save a great deal of anxiety for many women and will reduce the overall cost of breast cancer screening while improving its accuracy.
Results of earlier clinical studies indicate that diagnostic breast tomosynthesis improves the ability to analyze lesion margins and distinguish malignant from benign tumors. This improved diagnostic information results in better identifying a correct target for biopsy, helps analyze tumor margins and the extent of breast cancer while helping to reduce the overall number of biopsies performed.